Wicked Cool Stuff

Dominick Gallegos, Civil 3D Technical Marketing Manager for Autodesk, shares his unique perspective and ideas on the functionality and use of Civil 3D for a range of different project types.

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posted 12/11/06 by Anthony Governanti How do you grade?
I had an interesting conversation via IM the other day with the Civil 3Diva. We were discussing the different ways to grade a commercial site, and we had some differences of opinion when it came down to some of the methods you can use in Civil 3D.

Dana has become a big proponent of using the corridor model to do the bulk of the site grading, and I am a bit more of a traditionalist in that I make heavy use of feature lines and what I call "reference" surfaces. So we went back and forth as to which way is better, and it dawned on us that this conversation should probably be more public.

So we've decided to each post about our methods to our respective blogs, and let you decide which one is better for you. In the end, I think it will depend on the site conditions, and your familiarity with the tools available. Either way, it should make for good conversation, at least in cyberspace.

The site:
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This site is a fairly typical commercial development, with large parcels for industrial buildings and a simple road that splits the property in half. Here I have a parking lot laid out with an entrance to the road, and I need to make some decisions for how I will grade the lot.

The Flow:
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I've decided to split the parking lot in half from east to west, and will make a grade line that runs parallel to the parking spaces. As you can see, I'll flow the water to the east (away from the proposed building pad that will be on the west side of the parking lot) and will tilt the lot 1% down from the north and 2% down from the south.

The Setup:
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With the general flow conditions determined for my site, I can create some reference elements that I will use to base my grading on. I take my flowline and convert that to a feature line, and set grade on it using the elevation editor. I then use the Stepped Offset feature line command to offset this line to the north and south 150 feet, at 1% and 2% respectively. I add these feature lines to a new surface, which is my reference surface for my site. It dictates the flow characteristics for the overall conditions of my design.

Site Topology - this is where the lessons we've learned on site topology are crucial; we need to keep the feature lines for our reference surface is a separate site from our lot grading feature lines. I make it a habit to create two sites as soon as I start my grading; one for reference lines, and one for my actual site grading.

The Grading:
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Feature Lines created and then graded from the reference surface.

Now that I have this reference surface, I simply project all my parking lot feature to it, and they become "graded". This is where a lot of time is saved, in that I don't have to set any points, or project any slopes; I simply just grab the elevations from my reference surface, and BAM, my lot is graded for me. I then add these lines to a new surface, and we can start to see the design coming together.

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Feature lines added to a new surface.

Two tips here; when you convert the linework to Feature lines, make sure to uncheck the option for erasing existing object; we'll need this linework again later if and when we do some site visualization. Two, when you get elevations from surface for the new feature lines, make sure to uncheck the option to insert intermediate grade points as this will save a lot of processing time by eliminating a vertical point being added to every triangle crossing point.

Next I create all my curb lines by again using the stepped offset feature line command. I use a distance of 6 inches and an elevation difference of 6 inches.
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Now I finish the design by adding the curb lines to the surface, as well as projecting the outer limits of my parking lot to existing ground using the grading tools.

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Final Parking Lot surface.

So I hope you can see that by using the feature line tools and the surface capabilities of Civil 3D, you can do commercial site grading. By using my method of feature lines and a reference surface you can quickly grade the site, and if anything changes, you have the flexibility to either make adjustments to individual features using the feature lined editing tools, or to the entire site by changing the reference surface.

With a little effort on the visualization side you can quickly create powerful rendering of your work.
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Look for Dana's version of this site to be posted over at Civil3D.com sometime soon.

So I leave it up to you which method you prefer; just know that Civil 3D is capable of doing commercial site grading - its all in the tools and methods you use.

Till next time,
Cheers,
AG

7 comments In Wicked Cool Stuff > Wicked Cool Tips

User Comments

  • I'm going to put in my .02 All these techniques you and Dana and many others offer are outstanding. The thing I've encountered is the real world designs I've had to do are much more complicated than any I've seen. Maybe I just have a little trouble going that last yard to bridge that design gap. Keep up the good work!!

    Posted 12/12/2006 9:48 AM by Fred Mitchell

  • I would agree with Fred that the designs I encounter are much more complex than this, but appreciate the concepts from both. I have found that the wonderful thing about Civil3D is that you can use both and grading groups simultaneously with great results if you follow a few rules about sites and data reference. I have found it benefital to create my parking lots with feature lines and the curbs using corridors, because I can use regions to place the type of curb I need in a specific situation.
    Thanks

    Posted 12/14/2006 2:31 AM by Eric Gates

  • I'd really like to see some of the more comlex designs you refer too. Is there a way to send a DWF or Drawing?

    For me, I've always tried to strike a balance between showing something in a simple enough way that the concept comes through, but not so simple that it can't be applied.

    AG
    anthony.governanti@atuodesk.com

    Posted 12/14/2006 12:52 PM by Anthony Governanti

  • In the area that I live, we have a lot of relief over a site. So once you stick a building in the middle of that parking lot, have an entrance coming down at 10%, a HC stall at 2%, it gets a little tricky making the surface pretty. I've tried the corridor model, and I like it for certain things. I've found it works pretty well for the curb around the exteriors of the property. But for the curb around the building, internal parking islands, etc, I like feature lines. I think a combination of the two is best. With the feature lines' ability to reference a surface, it's much nicer than LDT.

    mjwoodruff@cadtimes.com

    Posted 12/15/2006 7:00 AM by Michael Woodruff

  • A variation on the theme.

    Use a reference surface to meet the design criteria (3% max grade and hit the elevation of the entrances) in separate site.

    Setup a new site. Create an alignment along the middle of the parking lot. Profile the alignment to the ref. surface and create a FG profile along the reference surface profile. Create a dummy assembly with no sub assemblies. Create the cooridor.

    Create an alignment along the inside edge of the curb and gutter. Profile the alignment to the reference surface. Define an assembly as a curb with the insert point at the inside edge of the curb, a link to get a 5% grade away from the curb for a ways and then a slope to the existing surface. Add the curb alignment as a baseline, the reference surface grade as the profile and the curb assembly as the assembly for the baseline. Repeat for other side of curb. Presto, Instant parking lot. For this project the baselines cross the centerline.

    I learned to lock the reference surface to preven "Where the &#@?/ did the parking lot go!" Using Dana's marked point method might make the surface a little smoother.

    Posted 12/16/2006 1:18 PM by Bryan Parker

  • the corridor method that i use (and mentioned by bryan here in the comments) tends to allow for more complex designs that go through more iterations. they are more complicated to set up- but less intensive to revise than using feature lines. anthony's method works best for cases where it is "once and done", meaning it is so straightforward you don't have any revisions.

    ie- if my design intent changes in AG's example, i have at least two feature lines on each island to revise/edit, plus a lot of other things. if i had made my curbs as baselines, i can those two feature lines (as well as additional features) react with the changing of one profile per island.

    or if you get slicker and better at applying assemblies, you can cut that number way down.

    more on civil3d.com soon....

    Posted 12/17/2006 11:33 AM by Dana Probert

  • My approach to grading is similar to yours, but I'm having difficulty using the feature lines to grade. When I use the stepped offset command (or copy, or move to site, actually any command) the Elevation Points that I added to the source feature line (green circles) disappear, and the offset (or copied) line is a straight grade from beginning to end. Is this a bug, a setting or am I doing something wrong?

    Posted 3/3/2008 8:28 AM by John Rauch